1. Field
The following description relates to a PIN diode and a manufacturing method thereof, and an x-ray detector using the PIN diode and a manufacturing method thereof. More particularly, the following description relates to a PIN diode configured to include a lower electrode, a PIN structure consisting of a P layer, a I layer, and a N layer electrically connected to the lower electrode, and an upper electrode, wherein a size of the PIN structure and a size of the upper electrode substantially correspond to each other so as to maximize a fill factor, and a manufacturing method thereof, and an x-ray detector using the PIN diode and a manufacturing method thereof.
2. Description of Related Art
Generally, x-rays have short wavelengths, and thus may easily penetrate an object. The amount of penetration of such x-rays depends on the density inside the object.
In other words, the inner state of the object can be observed indirectly based on the amount of x-rays that penetrated the object.
An x-ray detector is an apparatus for detecting an amount of x-rays that penetrated an object. The x-ray detector may detect an amount of penetration of x-rays, and display an inner state of the object through a display apparatus.
Generally, such an x-ray detector is used as a medical inspection apparatus, or a nondestructive inspection apparatus and the like.
The x-ray detector consists of a lower electrode, a PIN structure including a P layer, I layer, and N layer formed above the lower electrode, and an upper electrode formed above the PIN structure.
Herein, instead of being separately provided, the lower electrode may be made of a source electrode or a drain electrode of a thin film transistor. In a case where the lower electrode is separately provided, it may be configured to be electrically connected to a source electrode or a drain electrode of a thin film transistor through a contact hole.
FIG. 1 is a schematic diagram of a conventional x-ray detector. Referring to FIG. 1, the x-ray detector is provided with a thin film transistor that includes a gate electrode 110, a drain electrode 111, source electrode 112 and active pattern 13 on a substrate 100, and a lower electrode 120 electrically connected to the drain electrode 111 through a first contact hole 115 of a first protection film 114 formed above the drain electrode 111. The lower electrode 120 serves as an N side electrode.
Above the lower electrode 120, a PIN structure 130 is formed that includes an N type semiconductor pattern 131 formed on the lower electrode 120, an intrinsic semiconductor pattern 132 formed on the N type semiconductor pattern 131, and a P type semiconductor pattern 133 formed on the intrinsic semiconductor pattern 132.
For example, the N type semiconductor pattern 131 is made of Ni+a-Si, the intrinsic semiconductor pattern 132 is made of a-Si, and the P type semiconductor pattern 133 is made of P+a-Si.
Furthermore, the intrinsic semiconductor pattern 132 serves to absorb light being applied from outside and to generate electrons, and the P type semiconductor pattern 133 is formed to be as thin as possible so as to maximize the light penetration rate.
Furthermore, the upper electrode 140 is made of a transparent electrode material and is formed above the PIN structure 130.
Meanwhile, the thin film transistor, the lower electrode 120, the PIN structure 130 and the upper electrode 140 form one sensing pixel.
Above the upper electrode 140, a second protection film 150 having a second contact hole 151 is formed, and above the second protection film 150, bias wires are formed.
The bias wires include a main data wire 161, shield layer 162, and bias wire 163 and so on.
Above a result product where the bias wires are formed, a third protection film 170 is formed, and above the third protection film 170, an organic insulation layer 180 is formed.
A scintillator layer for converting the light of x-rays is attached to or formed on the organic insulation layer 180 by a depositing process.
Herein, the upper electrode 140 is desirably formed such that it corresponds to the size of the PIN structure 130 in consideration of the adhesive force with the PIN structure 130 and the optical conversion efficiency.
FIG. 2 is a diagram illustrating a conventional manufacturing method of an x-ray detector. Referring to FIG. 2, in the conventional manufacturing method of an x-ray detector, a thin film transistor (not illustrated) is formed on a substrate (not illustrated), and then a contact hole is formed on a protection film (not illustrated) formed above the thin film transistor, and then a lower electrode 120 is formed to be electrically connected to the thin film transistor through the contact hole.
Furthermore, above the lower electrode 120, a PIN layer 130A is deposited sequentially to form a PIN structure 130. Then, above the PIN layer 130A, an upper electrode layer 140A is deposited at a room temperature condition (about 23° C.).
Then, above the upper electrode layer 140A, a photo resist layer is deposited, and then exposed and developed to form a photo resist pattern 141.
Furthermore, using a wet etching process, the upper electrode layer 140A is etched to form an upper electrode 140.
The size of the pattern of the electrode formed by a wet etching process is generally smaller than that of the photo resist pattern 141. The extent of the reduced size is referred to as a CD Bias.
That is, the upper electrode 140 is excessively-etched than the photo resist pattern 141, and thus formed to have a smaller edge area and a CD Bias of about 2˜3 μm.
Then, using a dry etching process, the PIN layer 130A is etched having the photo resist pattern 141 as a mask so as to form the PIN structure 130, and the photo resist pattern 141 is removed thereby completing the process of forming the lower electrode 120, PIN structure 130, and upper electrode 140.
The said process forms the upper electrode 140 and PIN structure 130 using one photo resist pattern 141, and thus each profile is determined according to the CD Bias of the upper electrode 140 and PIN structure 130.
Herein, it is desirable to match the CD Bias of the upper electrode 140 to the CD Bias of the PIN structure 130 so that the size of the upper electrode 140 is almost substantially the same as the size of the PIN structure.
By doing this, it is possible to maximize an amount of conversion into electrical signals with a same amount of visible rays.
The bigger the CD Bias of the upper electrode 140, that is, the smaller the size of the upper electrode 140 compared to the size of the PIN structure 130, the smaller the fill factor of the PIN diode.
The fill factor is a ratio of a light receiving area of a pixel unit in the x-ray detector. The smaller the fill factor, the smaller the amount of conversion into electrical signals even with a same amount of visible rays, thereby deteriorating the performance of the x-ray detector.
Meanwhile, since the upper electrode 140 is deposited at a room temperature, it is problematic in that its adhesive force with the PIN structure 130 is low, thereby causing the upper electrode 140 to come off in a subsequent process.
Meanwhile, besides the said x-ray detector, any apparatus where a PIN diode structure including a lower electrode, PIN structure, and upper electrode is applied may have the same problem.